This invention pertains to labeling machines and, in particular, to a device for applying glue to the labels before they are applied to containers such as bottles.
The basic features of a labeling station of the type of interest herein are described in many prior patents such as U.S. Pat. No. 4,512,842. The labeling machine of the type described in this patent has a rotor turning about a vertical axis. A number of glue pallets or label pick-off elements are arranged about the periphery of the rotor and these elements are usually driven by a cam so that they oscillate through a limited angle as the rotor rotates. As the pallets are rotated in a circular path, they roll on and off of a rotating roller that is coated with a thin film of glue, thereby depositing a film on the pallets. As the pallets rotate past a magazine containing labels, they contact successively the unprinted or backside of the foremost label with a rolling action so that the label picks up glue from the pallet and adheres to the curved surface of the pallet. The labels are then rotated successively to a transfer cylinder from which they are picked up directly or through intermediate means by passing bottles which rotate as they move to wrap the label about the bottle. The curved pallets or pick-off elements necessarily develop considerable contact pressure on the glue roller to pick up a uniform coating of glue. The thickness of the film of glue on the roller is controlled with a scraper blade. The edge of the blade runs lengthwise of the roller so that film thickness can be controlled by adjusting the blade toward and away from the surface of the roller to establish a gap corresponding to the desired glue film thickness.
Labeling stations of the type just outlined comprise a metal housing, called a gear box, and a power driven shaft extends vertically from the gear box and projects relatively far out from the gear box for supporting the roller over essentially its entire length. No other support for the glue roller has heretofore been provided at the upper end, probably, because no one had conceived how the upper free end of the glue roller shaft could be supported without interfering with disassembly of the parts of the glue applicator which is necessary for cleaning purposes. Even if a drive shaft having what might seem to be a greater than necessary diameter is used to obtain the desired stiffness of the drive shaft, deflection of the drive shaft to some degree is caused by the pressure of the pick-off pallets on the roller. In other words, the lateral force applied to the glue roller by the contacting pallets acts through a substantial moment arm which deflects the glue roller out of parallelism with the scraper blade. As a result, an optimal uniform glue film on the roller and, hence, on the pallets and labels is not maintained. Moreover, the glue scraper itself and its support can be deflected as the result of the pressure of the glue in the gap between the roller and scraper in the free area of the support which results in a non-uniform glue film thickness.
A result of the above mentioned conditions is that the optimal most economical glue film thickness setting cannot be maintained for a long period of time and it is often unavoidable to operate with a substantially thicker glue film on the glue roller than would be required for good label adhesion. Those skilled in the art will, of course, be aware that the glue film thickness must be critically controlled or the labels will be inclined to slip or float on the surface of the bottles. Moreover, if the glue film thickness is greater than necessary to achieve optimum adhesion, a substantial amount of glue will be wasted. During a single machine run, many thousands of labels will be applied and it will be found that glue consumption can increase dramatically far above expectations if the film thickness is not critically controlled.